Herbivory and intraspecific competition in a stream caddisfly population

• Published in: Oecologia Vol. 73; no. 1; pp. 75 - 81
• Main Authors: Lamberti, G.A, Feminella, J.W, Resh, V.H
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-08-1987; Springer
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Average linear density; Biological and medical sciences; competition; Density; Ecological competition; feeding behavior; Freshwater; Freshwater ecology; Fundamental and applied biological sciences. Psychology; Helicopsyche borealis; Helicopsychidae; Insect larvae; Intraspecific competition; Larvae; Larval development; Periphyton; population density; Population ecology; Protozoa. Invertebrata; streams; Trichoptera; USA, California, Big Sulphur Creek; United States; Growth; Insecta; Trichoptera; California; North America; Freshwater environment; Phytophagous; Arthropoda; America; Intraspecific competition; Competitive feeding; Stream; Invertebrata; Competition; Helicopsyche; Herbivory; Periphyton
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00376980

Field experiments were conducted to assess the effects of different population densities of the herbivorous caddisfly Helicopsyche borealis on periphyton biomass and on its own growth rate in Big Sulphur Creek, a third-order stream in northern California, USA. Stream enclosures were used to vary grazer density from one-eighth to twice natural density (1/8X-2X) in two experiments (35 d and 60 d), which spanned the period of most rapid larval growth. Periphyton biomass and chlorophyll a were inversely related to grazer density. Grazer densities of 1/8X-1/2X moderately reduced periphyton when compared to an ungrazed control, whereas densities of 1X-2X greatly depleted periphyton. The growth rate of H. borealis larvae declined with increasing larval density. Growth rate was highest at densities of 1/8X-1/2X; larvae grew more slowly at 1X and showed no growth at 2X. Weekly supplementation of periphyton to 1/4X, 1X, and 2X densities significantly increased the final body mass of larvae at 1X and 2X (by 26% and 50%, respectively, compared to unsupplemented larvae) but did not change the body mass of larvae at 1/4X. These results suggest that periphyton is a limiting resource in Big Sulphur Creek and that H. borealis larvae compete exploitatively for that resource. Intraspecific competition may be an important, but often overlooked, feature of many herbivore populations in streams.